Casey Jones my friend went through a pretty similar situation. Don't wan't to be an asshole but since the divorce seemed to come out of no where and your mom started dating a guy soon after do you think she was cheating on your old man and he found out? That's what happened with my friend, it was his moms old high school friend as well.
What I lived was not a divorce, but my ex gf which I was during 3 years when we break up 4 years ago suddenly became insanely jealous about ex gfs of mine with who I had no contact or whatever, she spyied my fb and my emails just to found out some conversations from years ago and went crazy but then accepted those conversations where years old, even before knowing her etc..
Then one day she read something I written to a friend of mine about another girl (you know typical conversation between guys talking about a hot girl...) then proceed to erase me from her life in a couple minutes.
Blocked me on msn, fb, phone etc... A couple days before everything was more or less okay, then she disappeared. It was a shock for me because I never thought it would end like that, and not having any way to communicate with her from 100 to 0 in a couple days. It was fucking hard for me, until I get to meet other girls that made me forget her and realize how crazy that situation was.
A year after her erasing me from her life, I stumble across her with her new BF, who happened to be her ex BF (the one before me with who she was during 2 years or so). To this day I'm almost positive her fear about me were only a projection of her own desires to go back with her firt BF. Understanding that was a relief, because I got to understand that nothing I could have done or said would have changed anything, and it was better for everybody involved to end like that.
Now I'm happier than ever with my gf, and I've never met my ex again, and I don't give a fuck anymore.
First love is something powerful and some people keep thinking about it like it was the best feeling, the chosen one etc...
I have nothing to say about divorce, I think sometimes it's a new start for people. I hope everything turns out for the better everybody.